Methods of forming shape engineered orthodontic appliances

ABSTRACT

The present disclosure relates to shape engineered orthodontic appliances and methods for fabricating the same. Methods of the present disclosure may comprise modifying a first representation of a patient&#39;s teeth, wherein the modified representation compensates for a non-elastic deformation resulting from use or wear of the orthodontic appliance. Methods may further comprise defining teeth receiving cavities on the orthodontic appliance, wherein the teeth receiving cavities are shaped to receive and apply a resilient positioning force to the patient&#39;s teeth. Methods may also comprise defining exterior portions on the orthodontic appliance using the modified representation of the patient&#39;s teeth.

CROSS-REFERENCE

This application is a continuation application of U.S. application Ser.No. 15/660,892, filed Jul. 26, 2017, which is a continuation applicationof U.S. application Ser. No. 12/203,088, filed Sep. 2, 2008, theentirety of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of orthodontics.More particularly, the present invention relates to orthodonticpositioning appliances shaped to compensate for non-elastic deformationand related methods.

An objective of orthodontics is to move a patient's teeth to positionswhere function and/or aesthetics are optimized. Traditionally,appliances such as braces are applied to the patient's teeth by anorthodontist or dentist and the set of braces exerts continual force onthe teeth and gradually urges them toward their intended positions. Overtime and with a series of clinical visits, the orthodontist adjusts theappliances to move the teeth toward their final destination.

More recently, alternatives to conventional orthodontic treatment withtraditional affixed appliances (e.g., braces) have become available. Forexample, systems including a series of preformed shell appliances havebecome commercially available from Align Technology, Inc., Santa Clara,Calif., under the trade name Invisalign® System. An Invisalign® Systemshell appliance can be made from thin clear plastic and have teethreceiving cavities. In use, the shell appliance is placed over thepatient's teeth and is removable. Shell appliances are designed toimpart positioning or repositioning forces to the patient's teeth. Theimparted forces are resilient in nature and are associated withcorresponding appliance elastic deformation. When used to repositionteeth, a series of individual appliances are worn by a patient toelastically reposition the patient's teeth over time. When used toposition teeth, one or more identical shell appliances are worn torestrain a patient's teeth in their current arrangement.

While alternative orthodontic treatment systems using patient removablepositioning appliances represent a considerable advancement in the fieldof orthodontics, appliance design improvements remain of interest. Forexample, in some cases undesirable non-elastic deformation may occur dueto use of a shell appliance. Therefore, appliance design systems, aswell as related systems, that address and/or compensate for suchundesirable deformation would be beneficial.

BRIEF SUMMARY OF THE INVENTION

The present invention provides improved orthodontic positioningappliances and related methods. These improved appliances are shaped tocompensate for non-elastic deformation that may occur as a result ofappliance use. Significant appliance non-elastic deformation may degradethe performance of the appliance by reducing or eliminating desirablecontact forces between the appliance and a patient's teeth. By shapingthe appliance to compensate for expected or observed non-elasticdeformation, the amount of appliance performance degradation due tonon-elastic deformation is decreased. Appliances with decreasedperformance degradation may help to decrease treatment time and expense.

Thus, in one aspect, the present invention provides an orthodonticappliance having teeth receiving cavities. At least one of the cavitiescan include a portion shaped to compensate for non-elastic deformationthat may be due to a variety of reasons, such as appliance use.

The present invention further provides methods for fabricating anorthodontic appliance having teeth receiving cavities. Such a method caninclude receiving a representation of a patient's teeth in a selectedarrangement. An appliance can be fabricated based on the receivedrepresentation and can include one or more teeth receiving cavitieshaving a cavity portion shaped to compensate for non-elastic deformationdue to use of the appliance. Such methods can include various computerbased techniques and methodologies.

For a fuller understanding of the nature and advantages of the presentinvention, reference should be made to the ensuing detailed descriptionand accompanying drawings. Other aspects, objects, and advantages of theinvention will be apparent from the drawings and detailed descriptionthat follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a lower jaw and an orthodontic positioning appliance.

FIG. 2A illustrates a cross section of a tooth together with a crosssection of a orthodontic positioning appliance that is not showing signsof significant non-elastic deformation.

FIG. 2B illustrates a cross section of a tooth together with a crosssection of a orthodontic positioning appliance that is showing signs ofsignificant non-elastic deformation.

FIG. 3 illustrates a cross section of a tooth and a cross section of anorthodontic positioning appliance showing a modification in accordancewith an embodiment of the present invention.

FIG. 4A illustrates a cross section of a tooth and a cross section of anorthodontic positioning appliance in accordance with an embodiment ofthe present invention.

FIG. 4B illustrates the appliance and the tooth of FIG. 4A when theappliance is worn by the patient.

FIG. 5 is a block diagram illustrating the steps of a method fordefining an orthodontic positioning appliance in accordance with thepresent invention.

FIG. 6 illustrates a modified tooth external profile that can be used todefine the shape of a tooth receiving cavity in accordance with anembodiment of the present invention.

FIG. 7A is a block diagram illustrating the steps of a one method forfabricating an orthodontic positioning appliance in accordance with thepresent invention.

FIG. 7B is a block diagram illustrating the steps of another method forfabricating an orthodontic positioning appliance in accordance with thepresent invention.

FIG. 8 is a simplified block diagram of a data processing systemincorporating an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention described herein provides improved orthodontic positioningappliances and related methods. According to the present invention, anorthodontic positioning appliance can be shaped to compensate forappliance non-elastic deformation that can occur over time as a resultof use of the appliance. Appliance non-elastic deformation can occur dueto a variety of causes. For example, possible causes can includematerial creep and/or stress relaxation. Another exemplary cause isappliance expansion or contraction caused by hydration or temperaturechanges. Significant amounts of appliance non-elastic deformation mayreduce or eliminate desirable contact forces between the appliance andthe teeth, thereby degrading appliance performance. Appliances of thepresent invention can advantageously maintain higher levels of desirablecontact forces in the presence of significant amounts of non-elasticdeformation, thereby reducing performance degradation due to non-elasticdeformation.

Orthodontic positioning appliances of the present invention can bedefined and manufactured in a variety of ways, including using methodsdescribe herein. These appliances can be fabricated using both directand indirect methods. These appliances can also be modeled/designedusing computer implemented methods.

FIG. 1 shows one adjustment appliance 10 which is worn by the patient inorder to restrain and/or reposition a patient's teeth (e.g., teeth asillustrated in jaw 11). The appliance can include a shell (e.g.,polymeric shell) having teeth-receiving cavities that receive andresiliently restrain and/or reposition the teeth. In one embodiment, apolymeric appliance can be formed from a thin sheet of suitableelastomeric polymeric material, such as Tru-Train (e.g., 0.03 inch)thermal forming dental material (Tru-Train Plastics, Rochester, Minn.).An appliance can fit over all teeth present in an upper or lower jaw, orless then all of the teeth. In some cases, only certain teeth receivedby an appliance will be repositioned by the appliance while other teethcan provide a base or anchor region for holding the appliance in placeas it applies force against the tooth or teeth targeted forrepositioning. In some cases, many or most, and even all, of the teethwill be repositioned at some point during treatment. Teeth which aremoved can also serve as a base or anchor for holding the appliance as itis worn by the patient. Typically, no wires or other means will beprovided for holding an appliance in place over the teeth. In somecases, however, it may be desirable or necessary to provide individualanchors on teeth with corresponding receptacles or apertures in theappliance so that the appliance can apply a selected force on the tooth.Exemplary appliances, including those utilized in the Invisalign®System, are described in numerous patents and patent applicationsassigned to Align Technology, Inc. including, for example in U.S. Pat.Nos. 6,450,807, and 5,975,893, as well as on the company's website,which is accessible on the World Wide Web (see, e.g., the url“align.com”).

An appliance can be designed and/or provided as part of a set orplurality of appliances. In such an embodiment, each appliance may beconfigured so a tooth-receiving cavity has a geometry corresponding toan intermediate or final tooth arrangement intended for the appliance.The patient's teeth are progressively repositioned from their initialtooth arrangement to a final tooth arrangement by placing a series ofincremental position adjustment appliances over the patient's teeth. Theadjustment appliances can be generated all at the same stage or in setsor batches, e.g., at the beginning of a stage of the treatment, and thepatient wears each appliance until the pressure of each appliance on theteeth can no longer be felt or has resulted in the maximum allowabletooth movement for that given stage. A plurality of different appliances(e.g., set) can be designed and even fabricated prior to the patientwearing any appliance of the plurality. After wearing an appliance foran appropriate period of time, the patient replaces the currentappliance with the next appliance in the series until no more appliancesremain. The appliances are generally not affixed to the teeth and thepatient may place and replace the appliances at any time during theprocedure (e.g., patient removable appliances). The final appliance orseveral appliances in the series may have a geometry or geometriesselected to overcorrect the tooth arrangement, i.e., have a geometrywhich would (if fully achieved) move individual teeth beyond the tootharrangement which has been selected as the “final.” Such over-correctionmay be desirable in order to offset potential relapse after therepositioning method has been terminated, i.e., to permit movement ofindividual teeth back toward their pre-corrected positions.Over-correction may also be beneficial to speed the rate of correction,i.e., by having an appliance with a geometry that is positioned beyond adesired intermediate or final position, the individual teeth will beshifted toward the position at a greater rate. In such cases, the use ofan appliance can be terminated before the teeth reach the positionsdefined by the appliance.

Referring now to FIG. 2A, a cross-sectional illustration shows a tooth22 within its associated cavity of an orthodontic positioning shellappliance 20 that has not been modified to compensate for non-elasticdeformation. As shown, the cavity of the appliance 20 generally conformsto the outer surface of the tooth 22. In some cases, general conformancebetween the appliance 20 cavity and the tooth 22 is most optimal when anew appliance 20 is initially installed, where the appliance 20 shapehas not been distorted by any significant non-elastic deformation. Thisconformance provides generally continual contact between the cavity ofthe appliance 20 and the tooth 22. Forces can be transmitted from theappliance 20 to the tooth 22 at points of contact, which allows theappliance 20 to impart its positioning or repositioning forces to thetooth 22.

FIG. 2B illustrates the impact that appliance non-elastic deformationcan have on how well the appliance 20 cavity conforms to the exteriorsurfaces of a tooth 22. In some cases, the use of an appliance 20 canresult in non-elastic deformation that tends to change the interiorshape of the appliance cavities. Use of an appliance results in internalstrains associated with the external deflection of the appliance. Theseexternal deflections can occur during use of an appliance. For example,during installation and removal of the appliance the cavity openings canbe stretched, such as when passing over relatively wider portions ofsome teeth, such as molars, or the stretching can occur as a result ofthe method of insertion or removal. This stretching can be morepronounced in a direction normal to the arch, due to the relative lackof appliance cavity walls in the inter-proximal region between adjacentteeth. Internal strains in an appliance can also arise due to a varietyof additional reasons, such as from positioning/repositioning forcesimparted on the teeth by the appliance, or from expansion/contraction ofthe appliance due to appliance hydration or temperature changes.Appliance internal strains can result in non-elastic deformation due tomaterial creep and/or stress relaxation. Where significant amounts ofnon-elastic deformation have occurred, the appliance 20 cavity may bedistorted to a point where conformance with the exterior of the tooth 22is less than optimal. For example, one type of distortion is illustratedin FIG. 2B, which shows a cavity cross section that has experienced asignificant increase in width at the opening of the cavity. As shown,this increased width can lead to loss of contact between the appliancecavity and portions of the tooth, which may lead to a reduction inappliance performance.

FIG. 3 illustrates a cross section of an orthodontic positioningappliance 30 showing a modification in accordance with an embodiment ofthe present invention. As shown, the appliance 30 includes an upperportion 34 and a lower portion 36. In the embodiment shown, the lowerportion 36 is modified as shown in the dashed lines to compensate forexpected amounts of non-elastic deformation due to use of the appliance.Depending upon the particular circumstances, such as the particulartooth geometry, appliance geometry, and appliance material, differentamounts of non-elastic deformation may result due to use of theappliance over time. For example, where a tooth is significantly wideraway from the gingival margin than it is near the gingival margin, suchas for particular molars, higher levels of internal strain may occurduring installation and removal leading to higher levels of materialcreep and/or stress relaxation and resulting non-elastic deformation.Although larger or smaller amounts of maximum deformation are possible,in some cases levels of appliance non-elastic deformation may rangebetween zero and thirty percent of the initial dimension, with somecases ranging between five to twenty percent, and with some casesranging between ten and fifteen percent. In the embodiment shown, thewidth of the internal cavity has been decreased to the greatest extentnear the cavity opening, where the maximum amount of non-elasticdeformation is expected to occur. As shown, the width of the cavity inthe lower portion 36 has been decreased by a progressively smalleramount, thereby reaching no change in the width where the lower portion36 joins the upper portion 34. The progressive modification shown can bebeneficial in compensating for the appliance non-elastic deformationdepicted in FIG. 2B.

It should be appreciated that a wide range shape modification can bepracticed within the scope of the present invention. Particular shapemodifications may be beneficial to compensate for particular non-elasticdeformations observed or expected, which may arise due to a wide rangeof reasons, including the complex dental/appliance geometry. Particularshape modifications may also be beneficial to produce desiredforce/torque levels between the appliance and the patient's teeth. Assuch, the illustrated embodiment of FIG. 3 is just one of many possiblecompensating shape modifications that can be practiced in accordancewith the present invention. For example, as can be seen by comparing theembodiment of FIG. 3 with FIG. 2B, the modification of FIG. 3 generallyrepresents a complement of the deformation shown in FIG. 2B. Similarcomplementary shape modification can be practiced for each of the widerange of deformations that may occur as a result of appliance use. Ingeneral, shape modifications that can be practice are not limited toshape modifications used to compensate for observed or expectednon-elastic deformations, or to shape modifications used to producedesired force/torque levels. For example, shape modifications can alsobe practiced to compensate for other dimensionally relatedconsiderations, such as expansion or contraction due to appliancehydration or temperature changes.

Referring now to FIGS. 4A and 4B, a cross sections of a tooth 22 and anembodiment of an orthodontic positioning appliance 30 in conformancewith the present invention are shown. The embodiment shown incorporatesthe compensating shape modification as shown in FIG. 3. The shapemodification results in the cavity opening that is smaller than acorresponding width of the associated tooth. When the appliance worn,the interfacing surfaces of the tooth force the contacting appliancecavity surfaces outward. The resulting contact forces between the toothand the appliance cavity in FIG. 4B are greater than the resultingcontact forces between the tooth and the appliance in FIG. 2A due to thegreater imposed deflection on the appliance. As a result, the applianceembodiment of FIGS. 4A and 4B would have to experience greater amountsof non-elastic deformation before the gapping condition shown in FIG. 2Bwould result. This ability to tolerate increased amount of appliancenon-elastic deformation serves to increase the ability of the applianceto impart desired positioning/repositioning forces/torques to the teethduring its course of use by the patient.

Referring now to FIG. 5, an exemplary method 100 for defining anorthodontic positioning appliance in accordance with the presentinvention will now be described. It should be appreciated that themethod 100 can be practiced in a variety of ways. For example, themethod 100 can be computer implemented and employ three-dimensionalmodeling representations and techniques. The method 100 can also bepracticed using physical models, such as models based upon impressionsor scans of the patient's teeth. These models can be physicallymanipulated to produce a physical representation of the patients teethin a selected arrangement.

The method 100 starts with receiving a representation of the patient'steeth in a selected arrangement (step 102). The selected arrangement inparticular, and the representation in general, will depend upon thepurpose of the particular appliance being defined. Where the appliancewill be used to apply positioning forces to constrain a patient's teethin their current arrangement, the selected arrangement can correspond tothe current arrangement of the patient's teeth. Where the appliance willbe used to apply repositioning forces to move the patient's teeth fromtheir current arrangement toward a subsequent arrangement, the selectedarrangement will typically deviate from the current arrangement of thepatient's teeth. For example, the selected arrangement can generallycorrespond to a subsequent arrangement toward which the teeth are to berepositioned. The received representation, as modified by subsequentsteps in the exemplary method 100, forms a basis for the definition ofthe teeth receiving cavities of the appliance as described below.

In step 104, selected teeth of the received representation areoptionally modified. This optional modification can include any numberof the teeth, from one to all. A wide range of modifications arepossible. For example, the size of any number of teeth can be scaled bya desired amount. By decreasing the size of a tooth in therepresentation, the resulting cavity for the tooth will be smaller thanthe patient's actual tooth, thereby producing increasedinterference/contact forces between the cavity and the tooth. Similarly,increasing the size of a tooth in the representation will result in acavity larger than the patient's actual tooth, thereby producingdecreased contact between the cavity and the tooth. Scaling can also beused to compensate for expected levels of expansion/contraction of thealigner during use. For example, an aligner may expand or contract dueto changes in its temperature and/or hydration level as a result ofbeing exposed to the oral environment of the patient's mouth.

The teeth in the representation can also be locally modified, by eitheradding or removing material. Many local modifications are possible andcan be used to modify resulting force characteristics of the appliance.In general, local removal of material from the representation willresult in greater interference between the resulting cavity of theappliance and the local region of the tooth, thereby producing greatercontact forces.

Although not required, modified areas of the teeth can be limited toareas of the teeth that would contact the appliance cavities.Modification of areas of the teeth that do not contact appliancecavities, such as certain inter-proximal regions, would typically notimpact the shape of the resulting cavity. For example, where thereceived representation is digital, it may be possible to individuallyscale up each of the teeth in the representation. Such a scaling wouldlikely result in one or more virtual interferences between adjacentteeth in the inter-proximal area. These interfering areas can be ignoredduring the definition of the cavities of the appliance. Where thereceived representation is a physical model, modification by adding orremoving material would typically be limited to portions of the teeththat would contact the cavities of the appliance. For the embodiment ofthe appliance illustrated in FIGS. 3 and 4A, the areas of modificationwould generally be limited to buccal/lingual surfaces of the teeth awayfrom the crowns.

In step 106, the modified representation of the patient's teeth is usedto define preliminary cavities. Where method 100 is computerimplemented, step 106 can be accomplished in a variety of ways, such asby defining cavities using solid subtraction, or by defining cavitiesbased on exterior surface definitions of the teeth in the modifiedrepresentation. Where the modified representation is a physical model,the modified representation can be used as a positive mold/model overwhich a sheet of polymeric material can be formed, thereby formingcavities.

In step 108, the preliminary cavities can be optionally modified.Typically, step 108 would be used where no modification of selectedteeth in the received representation was accomplished in step 104.However, is should be appreciated that modifications can be made in bothstep 104 and step 108 and be within the scope of the present invention.As such, exemplary modifications that can be made in step 108 aregenerally complementary to corresponding modifications that can be madein step 104. For example, where as in step 104 material can be locallyremoved to increase resulting contact forces, in step 108 material couldbe added to achieve the same result. Where exemplary method 100 iscomputer implemented, material can be digitally added or removed fromthe cavity definition. Where method 100 is physically implemented,material can be physically added or removed from the physicalrepresentations of the cavities.

In step 110, exterior portions of the appliance are defined. A varietyof methods can be used depending on the general approach used topractice exemplary method 100. Where method 100 is computer implemented,exterior portions of the appliance can be digitally defined usingnumerous different approaches. In one exemplary approach, athree-dimensional solid model representation of teeth can be scaled up.The scaled representation of teeth can be the patient's teeth in aselected arrangement, or even a modified representation of the patient'steeth in a selected arrangement. Another approach would be to offsetexterior surfaces from a three-dimensional representation of teeth, orexterior surfaces from representations of the patient's teeth in aselected arrangement. Yet another approach would be to scale thereceived representation or the modified representation.

Referring now to FIG. 6, an exemplary local modification that can bepracticed in step 104 of FIG. 5 is illustrated. FIG. 6 illustrates across section of a molar that has been modified by removing material.The solid lines in FIG. 6 depict the cross section of the molar beforemodification. The dashed lines show the cross section as modified. Asshown, the portion of the molar away from the gingival margin has notbeen modified. The depth of material removal is greatest near thegingival margin, and becomes progressively less away from the gingivalmargin. The resulting tooth shape is in general conformance with themodified aligner cavity depicted in FIGS. 3 and 4A.

FIG. 7A illustrates an exemplary method 200 for fabricating anorthodontic positioning appliance in accordance with the presentinvention. In step 202, a representation of a patient's teeth in aselected arrangement is received. In step 204, selected teeth of thereceived representation are modified. Step 202 and step 204 are the sameas step 102 and step 104 of FIG. 5 respectively, so the foregoingdiscussion of these steps applies and will not be repeated here. Asdiscussed above with respect to step 102 and step 104, it should beappreciated that step 202 and step 204 can be computer implemented, orpracticed using physical representations, or combinations thereof. Instep 206, the appliance can be fabricated by forming a sheet ofpolymeric material over a physical model/mold corresponding to thedigital or physical definition resulting from step 202 and 204.

FIG. 7B shows another exemplary method 250 for directly fabricating anorthodontic positioning appliance. Method 250 can involve using adigital definition of the appliance to control a fabrication machine.Various known manufacturing processes can be used to directly fabricatean orthodontic positioning appliance. In one approach, the appliance isformed by a stereo-lithography fabrication machine, where resin isselectively hardened in the shape of the appliance definition.

FIG. 8 is a simplified block diagram of a data processing system 300embodying the present invention. Data processing system 300 typicallyincludes at least one processor 302 which communicates with a number ofperipheral devices via bus subsystem 304. These peripheral devicestypically include a storage subsystem 306 (memory subsystem 308 and filestorage subsystem 314), a set of user interface input and output devices318, and an interface to outside networks 316, including the publicswitched telephone network. This interface is shown schematically as“Modems and Network Interface” block 316, and is coupled tocorresponding interface devices in other data processing systems viacommunication network interface 324. Data processing system 300 could bea terminal or a low-end personal computer or a high-end personalcomputer, workstation or mainframe.

The user interface input devices typically include a keyboard and mayfurther include a pointing device and a scanner. The pointing device maybe an indirect pointing device such as a mouse, trackball, touchpad, orgraphics tablet, or a direct pointing device such as a touch screenincorporated into the display. Other types of user interface inputdevices, such as voice recognition systems, are also possible.

User interface output devices typically include a printer and a displaysubsystem, which includes a display controller and a display devicecoupled to the controller. The display device may be a cathode ray tube(CRT), a flat-panel device such as a liquid crystal display (LCD), or aprojection device. The display subsystem may also provide non-visualdisplay such as audio output.

Storage subsystem 306 maintains the basic programming and dataconstructs that provide the functionality of the present invention.Software modules used to implement the methods discussed above aretypically stored in storage subsystem 306. Storage subsystem 306typically comprises memory subsystem 308 and file storage subsystem 314.

Memory subsystem 308 typically includes a number of memories including amain random access memory (RAM) 310 for storage of instructions and dataduring program execution and a read only memory (ROM) 312 in which fixedinstructions are stored. In the case of Macintosh-compatible personalcomputers the ROM would include portions of the operating system; in thecase of IBM-compatible personal computers, this would include the BIOS(basic input/output system).

File storage subsystem 314 provides persistent (non-volatile) storagefor program and data files, and typically includes at least one harddisk drive and at least one disk drive (with associated removablemedia). There may also be other devices such as a CD-ROM drive andoptical drives (all with their associated removable media).Additionally, the system may include drives of the type with removablemedia cartridges. The removable media cartridges may, for example behard disk cartridges, such as those marketed by Syquest and others, andflexible disk cartridges, such as those marketed by Iomega. One or moreof the drives may be located at a remote location, such as in a serveron a local area network or at a site on the Internet's World Wide Web.

In this context, the term “bus subsystem” is used generically so as toinclude any mechanism for letting the various components and subsystemscommunicate with each other as intended. With the exception of the inputdevices and the display, the other components need not be at the samephysical location. Thus, for example, portions of the file storagesystem could be connected via various local-area or wide-area networkmedia, including telephone lines. Similarly, the input devices anddisplay need not be at the same location as the processor, although itis anticipated that the present invention will most often be implementedin the context of PCs and workstations.

Bus subsystem 304 is shown schematically as a single bus, but a typicalsystem has a number of buses such as a local bus and one or moreexpansion buses (e.g., ADB, SCSI, ISA, EISA, MCA, NuBus, or PCI), aswell as serial and parallel ports. Network connections are usuallyestablished through a device such as a network adapter on one of theseexpansion buses or a modem on a serial port. The client computer may bea desktop system or a portable system.

Scanner 320 is responsible for scanning impressions or casts of thepatient's teeth obtained either from the patient or from an orthodontistand providing the scanned digital data set information to dataprocessing system 300 for further processing. In a distributedenvironment, scanner 320 may be located at a remote location andcommunicate scanned digital data set information to data processingsystem 300 via network interface 324.

Fabrication machine 322 fabricates dental appliances based onintermediate and final data set information received from dataprocessing system 300. In a distributed environment, fabrication machine322 may be located at a remote location and receive data set informationfrom data processing system 300 via network interface 324.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

What is claimed is:
 1. A computer-implemented method, the methodcomprising: receiving a first representation of a patient's teeth in afirst arrangement; modifying one or more areas of the firstrepresentation to create a modified representation of the patient'steeth, wherein the modified representation compensates for a non-elasticdeformation due to use of an orthodontic positioning appliance for thepatient's teeth; defining first cavities of the orthodontic positioningappliance using the modified representation of the patient's teeth,wherein the first cavities correspond to the one or more areas of thefirst representation and wherein the first cavities are part of aplurality of tooth receiving cavities of the orthodontic positioningappliance configured to move the patient's teeth from the firstarrangement toward a second arrangement; defining exterior portions ofthe orthodontic positioning appliance using the modified representationof the patient's teeth; and providing instructions to fabricate theorthodontic positioning appliance based on the first cavities and theexterior portions.
 2. The method of claim 1, further comprisingfabricating the orthodontic positioning appliance using the instructionsto fabricate the orthodontic positioning appliance.
 3. The method ofclaim 1, further comprising using the instructions to form a mold of thepatient's teeth.
 4. The method of claim 1, further comprising: using theinstructions to form a mold of the patient's teeth; and forming a sheetof polymeric material over the mold to fabricate the orthodonticpositioning appliance.
 5. The method of claim 1, further comprisingdirectly fabricating the orthodontic positioning appliance using theinstructions to fabricate the orthodontic positioning appliance.
 6. Themethod of claim 1, further comprising selectively hardening a polymericmaterial used to form the orthodontic positioning appliance using theinstructions to fabricate the orthodontic positioning appliance.
 7. Themethod of claim 1, wherein the non-elastic deformation comprises adeformation between zero and thirty percent of an initial appliancedimension.
 8. The method of claim 1, wherein at least one of the firstcavities is a molar tooth receiving cavity configured to receive a molarof the patient's teeth.
 9. The method of claim 1, wherein: at least oneof the first cavities is a molar tooth receiving cavity configured toreceive a molar of the patient's teeth; the molar has a first width nearthe gingival margin of the molar and a second width away from thegingival margin of the molar; and the second width is greater than thefirst width.
 10. The method of claim 1, wherein the non-elasticdeformation is due to internal strain due to installation, removal, orsome combination thereof, of the orthodontic positioning appliance. 11.The method of claim 1, wherein the non-elastic deformation is associatedwith material creep, stress relaxation, or some combination thereof, ofa polymeric material used to form the orthodontic positioning appliance.12. The method of claim 1, wherein modifying one or more areas of thefirst representation to create the modified representation of thepatient's teeth comprises decreasing a width of an internal cavity ofthe orthodontic positioning appliance near an opening of the internalcavity.
 13. The method of claim 1, wherein the modified representationof the patient's teeth corresponds to a complement of the non-elasticdeformation.
 14. The method of claim 1, wherein at least one of theplurality of tooth receiving cavities comprises an upper portion shapedto match a contour of an occlusal surface of the patient's tooth. 15.The method of claim 1, wherein at least one of the plurality of toothreceiving cavities comprises: an upper portion shaped to match a contourof an occlusal surface of the patient's tooth; and a lower portionhaving a proximal end beginning at the upper portion and a distal endterminating near the patient's gingival margin when the orthodonticpositioning appliance is worn by the patient.
 16. The method of claim 1,wherein at least one of the plurality of tooth receiving cavitiescomprises: an upper portion shaped to match a contour of an occlusalsurface of a patient's tooth; a lower portion having a proximal endbeginning at the upper portion and a distal end terminating near thepatient's gingival margin when the orthodontic positioning appliance isworn by the patient; and wherein the lower portion of the at least oneof the plurality of tooth receiving cavities is shaped to apply adesired force or torque to the patient's tooth.
 17. The method of claim1, wherein the first arrangement comprises a current arrangement of thepatient's teeth.
 18. The method of claim 1, further comprising scanningthe patient's teeth to obtain a current arrangement of the patient'steeth.
 19. The method of claim 1, further comprising: scanning thepatient's teeth to obtain a current arrangement of the patient's teeth;and identifying a plurality of stages of a treatment plan to move thepatient's teeth from the current arrangement toward a targetarrangement, wherein the plurality of stages define a plurality ofintermediate arrangements between the current arrangement and the targetarrangement; and wherein the first arrangement is the currentarrangement or one of the plurality of intermediate arrangements.
 20. Asystem comprising: one or more processors; and memory coupled to the oneor more processors, wherein the memory is configured to storecomputer-executable instructions that, when executed by the one or moreprocessors, cause the system to implement a computer-implemented methodcomprising: receiving a first representation of a patient's teeth in afirst arrangement; modifying one or more areas of the firstrepresentation to create a modified representation of the patient'steeth, wherein the modified representation compensates for a non-elasticdeformation due to use of an orthodontic positioning appliance for thepatient's teeth; defining first cavities of the orthodontic positioningappliance using the modified representation of the patient's teeth,wherein the first cavities correspond to the one or more areas of thefirst representation and wherein the first cavities are part of aplurality of tooth receiving cavities of the orthodontic positioningappliance configured to move the patient's teeth from the firstarrangement toward a second arrangement; defining exterior portions ofthe orthodontic positioning appliance using the modified representationof the patient's teeth; and providing instructions to fabricate theorthodontic positioning appliance based on the first cavities and theexterior portions.